1. Field of the Invention
The present invention generally relates to a keypad assembly for an electronic device, and in particular, to a keypad assembly in which key buttons of the electronic device each include at least one optical filtering layer that changes the color of an input light wavelength by reacting or not reacting to the light wavelengths generated from at least two light emitting devices.
2. Description of the Related Art
Generally, a “portable communication apparatus” refers to an electronic apparatus which provides electrical communication between users and service providers. As examples of the portable communication apparatus, there are HHPs (hand held phones), CT-2 cellular phones, digital phones, PCS (personal communication service) phones, and PDAs (personal digital assistants). Conventional portable communication apparatuses may be classified in various types according to their appearance. For example, wireless terminals are classified into bar-type wireless terminals, flip-type wireless terminals, and folder-type wireless terminals according to their appearance. The conventional portable terminals are equipped with antenna devices, data input/output devices, and data transmission/reception devices. As the data input/output devices, keypads allowing data input through a finger press task are generally used.
A keypad used for data input includes a plate-shaped elastic pad, a plurality of key buttons on the top surface of the elastic pad, having characters printed thereon, and a plurality of protrusions on the bottom surface of the elastic pad. The portable terminals generally include a plurality of (typically 15-20) light emitting devices for backlighting the key pad.
FIG. 1 is a cross-sectional view of a conventional keypad assembly 1. The keypad assembly 1 includes a keypad 2, a switch board 3, and a plurality of Light Emitting Diodes (LEDs) 4.
The keypad 2 includes an elastic pad 2a that is made of a flexible material (e.g., rubber) and is plate-shaped, a plurality of key buttons 2b that are formed on the top surface of the elastic pad 2a and has numbers and characters printed thereon, and a plurality of protrusions that are formed on the bottom surface of the elastic pad 2a. 
Each of the protrusions 2c is arranged at the center of each of the key buttons 2b and a plurality of grooves 5 may be formed in the bottom face of the elastic pad 2a. The grooves 5 are arranged around the protrusions 2c in such a way to avoid interference caused by the LEDs 4 and the protrusions 2c. 
The switch board 3 includes a plate-shaped Printed Circuit Board (PCB) and a plurality of dome switches 3a formed on the top surface of the PCB facing the keypad 2.
The LEDs 4 are amounted on the top surface of the PCB and are positioned to be covered by the grooves 5 of the elastic pad 2a. 
If a user presses one of the key buttons 2b, a portion of the keypad 2 under the pressed key button 2b is transformed towards the switch board 3 and thus the protrusion 2c included in the transformed portion presses the dome switch 3a. A contact member 6 included in the dome switch 3a electrically contacts the protrusion 2c. 
For operations of the dome switches 3a, the LEDs 4 cannot be positioned under the key buttons 2b. Since a light A1 output from each of the LEDs 4 passes through the elastic pad 2a and illuminates each of the key buttons 2b in the form of a square, the illumination of the key button 2b is non-uniform and dark.
If a large number of LEDs 4 are installed to uniformly and brightly illuminate the key buttons 2b, power consumption increases. Moreover, due to a large number of parts, the time required for the assembly of a terminal and manufacturing cost of the terminal increase.
To address the problems, a keypad assembly including a light guide plate and reflecting patterns has been developed as shown in FIG. 2.
FIG. 2 is a cross-sectional view showing a light guide plate 20 and a plurality of reflecting patterns 40 in a conventional keypad assembly 10. Referring to FIG. 2, the keypad assembly 10 includes the light guide plate 20 through which a light moves, a plurality of key buttons 30 that are formed on the top surface of the light guide plate 20 and have numbers and characters printed thereon, the reflecting patterns 40 that are formed on the bottom surface of the light guide plate 20 and reflect the light A1 moving through the light guide plate 20 towards the key buttons 30, protrusions 50 under the reflecting patterns 40, a plurality of light emitting devices 70 that provide the light A1 to the light guide plate 20, and a switch board 60 including dome switches 80.
The single light guide plate 20 is provided for the illumination of the entire key buttons 30.
As such, the entire key buttons 30 can be illuminated using the light guide plate 20, but the numbers and characters printed on the key buttons 3 cannot be separately illuminated. As a result, the utility of the numbers and characters of the key buttons 30 may be degraded in some modes of the terminal.